1. Technical Field
This invention relates generally to chemical mechanical polishing (CMP) tools and in particular to a device for injecting slurry onto the polishing pad of a chemical mechanical polishing tool.
2. State of the Art
Chemical Mechanical Polishing (CMP) slurry, together with polishing pads and diamond conditioner disks, form the key components of the equipment used to carry out CMP processes in recent years. These polishing pads and diamond conditioner disks have been produced and marketed by several vendors to standards of reliable quality and effectiveness. The function of the polishing pad is to cut away and polish the wafer surface in conjunction with the slurry. As they accomplish this function, the polishing pads themselves become smooth and lose effectiveness in their capacity to polish the wafer surface. The function of the diamond conditioner disks, the surface facing the polishing pad of which is covered with small embedded diamonds or other hard substance, is to cut into and roughen the polishing pad surface during polishing so that it is continually being roughened as the wafer smoothes it. This way the effectiveness of the polishing pad is maintained relatively constant. The function of the slurry is to deliver continuously the mechanical abrasive particles and chemical components to the surface of the wafer and to provide a means of removing reaction products and wafer debris from the polishing surface. There are several varieties of slurry of varying effectiveness and properties known to the art. At present, for the most common type of CMP tool, the rotary polisher, slurry is applied at a constant flow rate onto the rotating polishing pad using a simple delivery tube, nozzle or spray bar. Fresh slurry flows away from the application point(s) under the influence of gravity and centripetal acceleration and becomes mixed with used slurry or slurry that has passed between the polishing pad and wafer and been involved in polishing. Old slurry, besides being chemically “spent”, additionally contains the debris from wafer, conditioner and pad. If the old slurry reenters the gap between the wafer and the polishing pad and is exposed to the wafer surface, this can lead to increases in contamination and defectivity. It is therefore important to remove the debris of polishing, and by extension used slurry, from the polishing pad quickly after it is generated and to the greatest extent possible not reintroduce it under the wafer. Thus there is a need for a device for injecting slurry onto the polishing pad surface, which also removes old slurry and does not allow the old slurry to be mixed with the new slurry.